It has heretofore been proposed to measure concentrations of water, oil (fat), protein and/or starch (carbohydrates) in food products, such as dairy, meat, fruit and grain products, using infrared and near-infrared quantitative analysis techniques. "An Introduction to Near-Infrared Quantitative Analysis," presented by R. D. Rosenthal at the 1977 Annual Meeting of the American Association of Cereal Chemists, surveys the basic technology in which infrared energy is directed onto a material sample at a number of different wavelengths selected as a function of absorption characteristics of the material constituents of interest, and constituent concentrations are obtained as a function of energy transmitted through or reflected by the sample at the various selected wavelengths. In one device illustrated in the Rosenthal paper, a number of optical filter elements are carried by a flat disc positioned between a light source and the sample. The disc is incrementally rotated to bring each filter in turn into alignment between the light source and the sample, and a detector is positioned on the opposite side of the sample to measure energy transmitted through the sample. The optical data readings are processed employing conventional multiple linear regression analysis techniques to obtain concentration readings of the various constituents. U.S. Pat. Nos. 4,415,809 and 4,447,725 disclose apparatus for measuring concentrations of moisture, fat, protein and lactose in dairy products See also U.S. Pat. Nos. 4,193,116, 4,253,766 and 4,627,008.
In apparatus of the subject character heretofore proposed, thermal-type optical detectors have generally been employed. Operating characteristics of detectors of this type require that energy to be measured be incident thereon for a substantial time, on the order of one-half second, for the thermal properties to stabilize and thereby permit reliable measurements to be obtained. Where the art has proposed use of detectors having more rapid optical response characteristics, the artisan has continued to employ previous illumination techniques. Consequently, substantial time is required to obtain a measurement at each preselected measurement wavelength.
Another problem characteristic of the art lies in limitations imposed on the number of available measurement wavelengths. That is, the number of available wavelengths has generally been limited by size of the filter-holding disk, which in turn is limited by available space. A change in desired wavelengths requires a physical change of filters, a time-consuming and exacting operation, particularly where the filter must be "tuned" to desired wavelength.
It is therefore a general object of the present invention to provide apparatus for quantitative analysis of material samples, such as whole grains, that is of compact and economical construction, that is sufficiently versatile as to be employed in conjunction with a number of differing test materials, such as differing cereal grains, that does not require sample preparation, that includes capability for performing measurements at a substantial number of selectable wavelengths over the chosen near-infrared range, and that provides rapid material analysis with minimum operator intervention and without sacrifice of measurement accuracy.